In Situ Controllably Self‐Assembled CoFe‐TDPAT Metal–Organic Framework Nanosheet Arrays on Iron Foam as Highly Efficient Bifunctional Catalytic Electrodes for Overall Water Splitting at Large Current Density

Abstract For the first time, a Co and Fe bimetallic metal‐organic framework (BMOF) nanosheet array (NSA) employing 5,5′,5′'‐(1,3,5‐triazine‐2,4,6‐triyl)tris(azanediyl)triisophthalic acid (H 6 TDPAT) as the organic ligand is in situ controllably self‐assembled on iron foam (IF). The obtained IF@CoFe‐TDPAT NSA exhibits an oxygen evolution reaction (OER) activity much superior to most reported catalysts and even Ru and Ir‐based ones and hydrogen evolution reaction (HER) activity higher than most metal‐organic framework (MOF)‐based catalysts. The excellent bifunctional activities are ascribed to the superhydrophilic (3D) vertically aligned, interconnected NSA of CoFe‐TDPAT MOF with in situ activated coordinatively unsaturated metal sites remarkably enhancing OH − and H 2 O adsorption, accelerating electron transfer and transport, and facilitating O 2 /H 2 diffusion. When adopted as a bifunctional electrode for overall water splitting, it achieves 300 mA cm −2 at 1.753 V and exhibits negligible current decay after 100 h. This performance is the highest of recently reported noble‐metal‐free water electrolyzers, and even much higher than those using commercial noble metal‐based catalysts. This work offers an economical, facile, and controllable strategy to fabricate low‐cost, highly efficient, and bifunctional BMOF nanostructured array electrodes for large‐current‐density water splitting, and also sheds light on the mechanisms for in situ self‐assembly and outstanding OER and HER performance of 3D free‐standing complex‐organic‐ligand‐based BMOF nanoarchitectures.